Introduction: We aimed to evaluate whether higher end-tidal alveolar dead space fraction (AVDSf) is associated with failure of a protocolized spontaneous breathing trial (SBT) in mechanically ventilated children with pediatric acute respiratory distress syndrome (PARDS). Secondary aims were determining whether children with high AVDSf were more likely to fail earlier in the SBT, or fail with hypercarbia, than children that failed with low AVDSf. Characterizing these relationships may offer insight into distinct phenotypes of SBT failure, potentially differentiating between ventilatory and non-ventilatory barriers to weaning. Methods: Secondary analysis of a single-center randomized control trial evaluating lung and diaphragm protective ventilation in PARDS (R01 HL134666). Patients with severe acute neurologic injury were excluded. Both intervention and control groups underwent daily protocolized SBTs upon meeting predefined oxygenation criteria, with SBT failure defined by standardized criteria. Patients were studied until they passed an SBT. All patients had continuous end-tidal CO2 (PETCO2) monitoring. Pre-SBT AVDSf was calculated using median values from the 12 hours prior to the SBT: AVDSf=(PCO2-PETCO2)/PCO2. We evaluated the association between AVDSf and SBT failure, early SBT failure (< 30 min) versus later failure (30-120 min), and failure related to hypercarbia (high PETCO2). Results: There were 553 SBTs from 199 distinct patients with required data for analysis. Median age was 4.5 years (IQR 1.2-12.0); 38.2% had chronic lung disease. Median oxygenation index (OI) at randomization was 7.7 (IQR 4.8-13.0). Of 324 failed SBTs, 57.4% were early failures and 19.1% failed with hypercarbia. A one standard deviation increase in AVDSf was associated with increased odds of SBT failure OR 1.33 (95% CI 1.08-1.65), p=0.0074 and remained significant OR 1.27 (95% CI 1.02-1.58), p=0.032 after adjusting for age, PRISM III score, and median pre-SBT OI in multivariable mixed effects logistic regression modeling. AVDSf was not more associated with early SBT failure than late failure, or failure related to hypercarbia. Conclusions: Higher AVDSf is independently associated with SBT failure regardless of failure phenotype. AVDSf may be an important marker to evaluate at bedside when assessing extubation readiness.
Rosenbaum et al. (Sun,) studied this question.